Initiator for a gas generator

ABSTRACT

An initiator employs ignition powder which can be manufactured easily, which can be handled safely, and which is stored in a cup of the initiator. Pins are inserted into and secured to holes of a header in the initiator. Distal end surfaces of the pins are flush with a distal end surface of the header; an insulative membrane is disposed so as to cover the distal end surface of one of the pins. When a high-voltage is applied between the pins, the membrane is destroyed and plasma is created. Further, when a subsequent low-voltage is applied between the pins, plasma is continuously generated. The ignition powder initiates its reaction by heat of the plasma.

BACKGROUND OF THE INVENTION

The present invention relates to an initiator suitable for building in a gas generator for an airbag apparatus or a seat belt pretensioner, ignition powder therefor, a method of activating the initiator, and the gas generator having the initiator.

An airbag apparatus mounted to a high-speed movable body such as an automotive vehicle is configured to inflate a bag-shaped airbag quickly with a gas generator so-called “inflator.” The gas generator is provided with a gas generating agent and an initiator for initiating a gas generating reaction of the gas generating agent. In the related art, the initiator includes ignition powder and a filament (bridge wire) as a resistive heat generating member for initiating the reaction of the ignition powder. (See e.g., U.S. Pat. No. 5,404,263, incorporated by reference herein in its entirety).

Referring now to FIG. 4, an example of the initiator in the related art will be described. The initiator 10 includes a substantially cup-shaped casing 12 opening at the rear end (the lower end in FIG. 4). In the casing 12, ignition powder 14 is stored. The rear end of the casing 12 is closed by an insulating material 16 formed of sintered glass or the like. Distal ends of a pair of electrodes 18, 20 penetrate through the insulating material 16 and are exposed in the interior of the casing 12.

A filament 22 is bridged between the distal ends of the electrodes 18, 20. Both ends of the filament 22 are welded to the distal surfaces of the electrodes 18, 20, respectively. The filament 22 is in contact with the ignition powder 14 in the casing 12.

The electrodes 18, 20 and the casing 12 are disposed apart from each other so as not to be brought into electrical contact with each other.

In the initiator 10 thus configured, one electrode 18 is connected to a positive electrode of a battery 26 of an automotive vehicle via a control circuit 24 having a voltage-increasing circuit or the like, and the other electrode 20 is connected (earthed) to a vehicle body of the automotive vehicle. The negative electrode of the battery 26 is connected (earthed) to the vehicle body of the automotive vehicle.

In case of emergency such as a vehicle collision, a switch element in the control circuit 24 is turned ON, and a voltage is applied from the battery 26 to the filament 22 via the respective electrodes 18, 20. Accordingly, the filament 22 generates heat, and hence the ignition powder 14 is ignited and initiates a reaction. By the reaction of the ignition powder 14, high-pressure gas or heat is generated, whereby the gas generating agent in the gas generator causes a gas generating reaction.

The ignition powder employed here includes, for example, a first ignition powder of mixture of lead styphnate and aluminum powder so as to surround the filament 22 and a second ignition powder of BKNO₃ or black powder disposed so as to surround the first ignition powder. The first ignition powder quickly initiates an exothermal reaction, and the second ignition powder initiates a reaction by heat of the first ignition powder to generate a high-pressure hot gas and fine grains.

Referring now to FIG. 5, an example of the gas generator having the initiator 10 will be described. A gas generator 30 includes a container having an outer shell having an upper housing 32 and a lower housing 34, and a cylindrical partition member 36 disposed in the outer shell. An end of the partition member 36 passes through an opening formed on the bottom surface of the lower housing 34 and projects downward. The inner peripheral surface of the opening and the outer periphery of the partition member 36 are welded by laser beam welding or the like. An ignition agent (booster propellant) 40 is stored in the partition member 36 and a gas generating agent (main propellant) 42 is stored on the outer peripheral side of the partition member 36.

The initiator 10 is disposed on one end of the partition member 36. When an ignition agent 40 is ignited by the initiator 10, gas is injected from an opening 44 of the partition member 36, and a large amount of gas is quickly generated, passes through a filter 46 formed of mesh or the like, and is injected through an opening 48 out of the gas generator 30, so that the air bag is inflated. FIG. 5 simply shows an example of the gas generator, and gas generators of the types other than that shown in the drawings may be employed.

In the initiator in the related art shown in FIG. 4 described above, it is required to control the length of the filament 22 or the conditions of welding precisely to keep the electric resistance of the filament 22 constant; this precision makes manufacturing difficult and correspondingly increases the cost thereof. In addition, the ignition powder 14 needs to be sensitive so as to be ignited even with a small exothermic energy of the filament. As a result, the sensitive ignition powder 14 needs to be treated with special care.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide: (a) an initiator in which the resistance heating element such as the filament is not used, (b) an ignition powder which can be easily and safely manufactured, treated, and used, and (c) a method of initiating the same. It is also an object of the present invention to provide a gas generator having such initiator.

According to an embodiment of the present invention, an initiator is provided. The initiator includes a casing, an ignition powder disposed in the casing, an electrode, and an insulating layer disposed in the casing so as to be in contact with the electrode on one surface and with the ignition powder on the other surface, wherein a reaction of the ignition powder is initiated by generating plasma by conducting electricity through the electrode.

The insulating layer is preferably formed of synthetic resin or a glass fiber mold of 10-300 μm in thickness. Preferably, the insulating layer is formed into a sheet-shape having holes smaller than the grain diameter of the ignition powder.

The ignition powder preferably includes MgAl alloy powder, KCl0₃ powder, and silicon resin binder.

The method of activating the initiator according to an embodiment of the present invention includes the steps of applying a high-voltage to the electrode of the initiator of the present invention to destruct the insulation, and subsequently, applying a low-voltage thereon.

Preferably, the high-voltage is at least 1 kV, and is applied for 0.1-50 μSec, and the low-voltage is 20-100 V and is applied for 50 μSec to 1 mSec.

The gas generator according to an embodiment of the present invention includes a gas generating agent, and the initiator according to the present invention.

In the initiator and the gas generator according to an embodiment of the present invention, when the voltage is applied to the electrode, plasma of high-temperature is generated in the casing. The ignition powder initiates reaction by heat of the plasma, and the gas generating agent in the gas generator is ignited and activated by high-pressure gas or heat generated by the reaction. This initiator is easy to manufacture since the insulating layer is provided instead of filament, and hence cost-effective manufacture with high process yield and low dispersions in quality.

As the energy of plasma is larger than heat-generating energy of the filament, ignition powder, which can be handled safely in comparison with the sensitive ignition powder used in the case where the filament is employed, can be used.

By disposing the synthetic resin or glass fiber mold of 10-300 μm in thickness so as to come into contact with the end surface of the electrode, the insulating layer can be formed easily at low costs.

When the insulating layer is a sheet-shaped layer having fine holes, it is susceptible to discharge. By making the diameter of the holes smaller than the diameter of the grains of the ignition powder, the ignition powder is prevented from entering the holes.

The ignition powder including MgAl alloy powder, KCl0₃ powder, and silicon resin binder can easily be treated and has a large calorific power.

By applying a high-voltage when activating the initiator to at least 1 kV (e.g., for example, to 1-5 kV), occurrence of insulation destruction is ensured and plasma is generated. The time period to apply the high-voltage may be as short as 0.1-50 μSec (e.g., for example, on the order of 1 μSec) and the power consumption is small. When the high-voltage is applied once, a plasma state may be maintained by only applying low-voltage such as 20-100 V (e.g., for example, on the order of 60 V). A low-voltage of 50 μSec-1 mSec (e.g., for example, on the order of 100 μSec) will be sufficient to maintain the plasma state.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.

FIG. 1 is a cross-sectional view of an initiator according to an embodiment of the present invention.

FIG. 2 is a not-to-scale graph showing a pattern of voltage application of the initiator versus time.

FIG. 3 is a cross-sectional view of an initiator according to another embodiment of the present invention.

FIG. 4 is a cross-sectional view of an initiator in the related art.

FIG. 5 is a cross-sectional view of a gas generator containing the initiator shown in FIG. 4.

FIG. 6 is a schematic view of an airbag apparatus according to an embodiment of the present invention.

FIG. 7 is a schematic view of a seat belt apparatus including a seat belt pretensioner according to an embodiment of the present invention.

DETAILED DESCRIPTION

Referring now to the drawings, embodiments of the present invention will now be described. FIG. 1 is a cross-sectional view of an initiator according to an embodiment of the present invention, and FIG. 2 is a not-to-scale waveform graph showing a voltage for activating the initiator.

In an initiator 50 shown in FIG. 1, a casing is formed by a cup 52, and a header 54 inserted into the entrance of the cup 52, and an ignition powder 58 is filled in the casing. In this embodiment, the cup 52 is shaped like a circular container formed of SUS304 steel or the like. The header 54 is substantially a disk-shaped or a cylindrical member formed of ceramic, and the cup 52 is fitted on the outer periphery thereof. The cup 52 is secured to the header 54 by being caulked around the edge thereof.

Cross-shaped grooves 52 a are formed on the outer surface of the distal end surface of the cup 52, so that the cup 52 cracks along the grooves 52 a when the ignition powder 58 is ignited and reacted. A ring-shaped gasket 56 is interposed between the cup 52 and the header 54.

Two bores penetrating through the thickness of the header 54 are formed at the center thereof. Electrode pins 62, 64 are inserted into the bores, respectively, and these pins 62, 64 are fixed to the header 54 by fixing material such as glass. The distal end surfaces of the pins 62, 64 are flush with the distal end surface of the header 54. A membrane 60 as an insulating layer is disposed so as to be aligned with the inner end surface of the cup of the header 54 and cover the distal end of the electrode pin 62.

The membrane 60 preferably is shaped like a sheet of 10-300 μm in thickness, and has a number of fine holes. The membrane 60 is preferably a synthetic resin sheet, more specifically, a fluorinated resin sheet having high heat resistance, or a glass fiber sheet mold.

The membrane 60 may be attached on the header 54 by an adhesive agent such as, for example, an acrylic, or silicon-contained material. The thickness of the adhesive agent is preferably on the order of 15-100 μm.

The ignition powder 58 may be only of ignition powder, or may be a mixture of ignition powder and particles of oxidizing agent. The ignition powder is not specifically limited, but may be a single metal such as Mg, Zr, Ti, W, B, Si, C, Be, Li, Al, V, CaC₂, Ca, Ce, La, and an alloy or a compound thereof. The oxidizing agent is not specifically limited, but may be KCl0₄, KCl0₃, Kl0₄, NH₄Cl0₄, NH₄NO₃ KNO₃, Fe₂O₃, Fe₃O₄, Sr(NO₃)₂, CuO, or NiO. The binder may include, for example, silicon-contained resin by about 0.5-3 percent by weight. By adding the silicon-contained binder, static resistance of about 25 kV may be provided.

The ignition powder preferably includes MgAl alloy powder, KCl0₃ powder, and silicon resin binder. The MgAl alloy can hardly be ignited in comparison with Zr, but it can easily be handled correspondingly. MgAl alloy exhibits higher heat value than Zr when ignited.

According to the initiator 50 thus configured, a high-voltage of about 3 kV is applied between the pins 62, 64 for about 1 μSec to generate plasma, and subsequently, a low-voltage of about 60 V is applied for about 100 μSec to maintain generation of plasma, as shown in FIG. 2. The ignition powder 58 initiates its reaction by heat of the plasma, and gas of high-pressure and high-temperature including fine grains is generated. When the ignition powder 58 includes grains of oxidizing agent, since the metallic particles rapidly start oxidative reaction by the oxidizing action of the oxidizing agent and generate heat, the reaction is promoted.

U.S. patent application Ser. No. 10/681,189 (incorporated herein by reference) discloses using a plasma to initiate a reaction.

According to an embodiment of the present invention, the filament (wire bridge) is not used, and hence the process steps of manufacture are significantly reduced.

During operation of the initiator 50, insulation of insulating layer (membrane 60) is destroyed by a pulsed high-voltage initially applied thereto, and the value of resistance is lowered by such destruction of insulation. Therefore, even with a low-voltage of about 60 V, electricity flows continuously. Therefore, it is no longer necessary to apply a high-voltage for a long time, and energy needed for ignition may be lower to about 1 mJ or below.

FIG. 3 is a cross-sectional view of the initiator 70 according to another embodiment. In this embodiment, an ignition powder 78 is filled between a cup 72 and a header 74.

The outer surface of the cup 72 is covered by a resin cover 75 formed of nylon, polypropylene, or the like. The rear side of the cup 72 and the rear end surface of the header 74 are covered with a resin mold 86 formed of nylon, polybutylenetelephtalate, or the like. The pins 82, 84 penetrate the resin mold 86 and project outward from the header 74.

In this embodiment, the header 74 is an annular-shaped member formed of SUS₃0₄ or the like, and the pins 82, 84 are inserted into the header 74 apart from each other so as not to come into contact with the header 74, and are fixed to the header 74 with an insulative fixing material 76 such as glass, hermetic seal, or the like. The distal end surfaces of the pins 82, 84 are flush with the distal end surface of the header 74. A membrane 80 is disposed so as to cover the distal end surface of the pin 82. The configuration of the membrane 80 is the same as the membrane 60.

In the initiator 70 thus configured, when a voltage is applied between the pins 82, 84 in the same pattern as that shown in FIG. 2, plasma is generated, and the ignition powder 78 initiates its reaction by heat of plasma.

The embodiments described above are examples of the present invention, and configurations other than those described above may also be employed. For example, the insulating layer may be provided so as to cover both of the pins 62, 64 or 82, 84.

When the header is formed of conductive material such as metal, it is also possible to provide only one pin and earth the header.

The initiator of the present invention may be applied to various gas generators. The gas generators may be built in various airbag apparatuses for a driver's seat, a front passenger's seat, a rear seat, side protection, head protection, pedestrian protection, and so on, or in a seat belt tensioner, or even in various detonators.

For example, as shown in FIG. 6, the initiator may be employed in a gas generator 30 positioned in an airbag apparatus including an inflatable airbag 90. Further by way of example, as shown in FIG. 7, the initiator may be employed in a gas generator 30 that is positioned in a seat belt retractor 120 for driving a spool 125 for pretensioning a seat belt 102. U.S. Pat. No. 6,363,722 (incorporated herein by reference) discloses an exemplary retractor. The seat belt retractor 120 may be part of a seat belt apparatus 100 which may additionally include a seat belt 102, a shoulder support 104, a tongue 106, and a buckle 108. The present invention also includes providing the improved initiator and gas generator in other known seat belt pretensioners.

The priority application, Japanese Patent Application No. 2003-289737, filed Aug. 8, 2003 including the specification, drawings, claims and abstract, is incorporated herein by reference in its entirety.

Given the disclosure of the present invention, one versed in the art would appreciate that there may be other embodiments and modifications within the scope and spirit of the invention. Accordingly, all modifications attainable by one versed in the art from the present disclosure within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is to be defined as set forth in the following claims. 

1. An initiator comprising: a casing containing ignition powder; an electrode; and an insulating layer disposed in the casing, wherein the insulating layer is in contact with the electrode on one surface and with the ignition powder on another surface, and wherein the initiator is configured so that reaction of the ignition powder is initiated by plasma generated by conducting electricity through the electrode.
 2. The initiator of claim 1, wherein the insulating layer comprises a synthetic resin or a glass fiber mold of about 10-300 μm in thickness.
 3. The initiator of claim 1, wherein the insulating layer is in the shape of a sheet and includes holes smaller than the grain diameter of the ignition powder.
 4. The initiator of claim 1, wherein the ignition powder comprises MgAl alloy powder; KCl0₃ powder; and silicon resin binder.
 5. The initiator of claim 2, wherein the ignition powder comprises MgAl alloy powder; KCl0₃ powder; and silicon resin binder.
 6. A method of activating an initiator including a casing containing ignition powder; an electrode; and an insulating layer disposed in the casing, wherein the insulating layer is in contact with the electrode on one surface and with the ignition powder on another surface, and wherein the initiator is configured so that reaction of the ignition powder is initiated by plasma generated by conducting electricity through the electrode, comprising the steps of: applying a high voltage to the electrode to destroy the insulating layer; and subsequently applying a low voltage to the electrode.
 7. The method of claim 6, wherein the step of applying the high voltage includes applying a voltage of at least about 1 kV.
 8. The method of claim 7, wherein the high voltage is applied for between about 0.1 μSec and about 50 μSec.
 9. The method of claim 6, wherein the step of applying a low voltage includes applying a voltage of between about 20 V and about 100 V.
 10. The method of claim 9, wherein the low voltage is applied for between about 50 μSec and about 1 mSec.
 11. A gas generator comprising: a gas generating agent; and an initiator for initiating gas generation reaction of the gas generating agent, wherein the initiator includes a casing containing ignition powder, an electrode, and an insulating layer disposed in the casing, wherein the insulating layer is in contact with the electrode on one surface and with the ignition powder on another surface, and wherein the initiator is configured so that reaction of the ignition powder is initiated by plasma generated by conducting electricity through the electrode.
 12. The gas generator of claim 11, wherein the insulating layer comprises a synthetic resin or a glass fiber mold of about 10-300 μm in thickness.
 13. The gas generator of claim 11, wherein the insulating layer is in the shape of a sheet and includes holes smaller than the grain diameter of the ignition powder.
 14. The gas generator of claim 11, wherein the ignition powder comprises MgAl alloy powder; KCl0₃ powder; and silicon resin binder.
 15. The gas generator of claim 12, wherein the ignition powder comprises MgAl alloy powder; KCl0₃ powder; and a silicon resin binder.
 16. A seatbelt apparatus comprising: a seat belt, a tongue for connecting to a buckle, and a pretensioner, wherein the pretensioner includes a gas generator and the gas generator includes a gas generating agent and an initiator for initiating gas generation reaction of the gas generating agent, the initiator including a casing containing ignition powder, an electrode; and an insulating layer disposed in the casing, wherein the insulating layer is in contact with the electrode on one surface and with the ignition powder on another surface, and wherein the initiator is configured so that reaction of the ignition powder is initiated by plasma generated by conducting electricity through the electrode.
 17. An airbag apparatus comprising: an airbag and a gas generator; wherein the gas generator includes a gas generating agent; and an initiator for initiating gas generation reaction of the gas generating agent; wherein the initiator includes a casing containing ignition powder, an electrode; and an insulating layer disposed in the casing, and wherein the insulating layer is in contact with the electrode on one surface and with the ignition powder on another surface, and wherein the initiator is configured so that reaction of the ignition powder is initiated by plasma generated by conducting electricity through the electrode. 